DESIGN ASPECTS.:OF.-SHALLOW .FOUNDATIONS IN LAYERED SOILS

Abstract

One of the most important geotechnical structures is the foundation which transfers the load coming from the superstructure to underlying soil subgrade without shear. Three dimensional tests were performed in laboratory to investigate the bearing capacity of a strip (100mm x 600mm) surface footing resting on sand overlying compacted clay and subjected to vertical central load. The parameters varied during tests are thickness of sand layer and compactness of sand. The soil used for testing was clay of intermediate compressibility (CI) (LL = 41.2%,PL= 21.0%) with an undrained shear strength of 65 KN1m2,which was .compacted in 25 mm thick layers at optimum moisture content of 19.9%. The sand used was poorly graded sand (SP) and having angle of internal friction of 32° and 39°. It was placed by pouring and compacting using tamper. A total of thirty two tests were conducted, with varying the top layer (sand layer) thickness below the base of the footing. In each test, loads and settlements, were measured. Computations and plots were made and conclusions were drawn giving the effect of H113 (H1= sand layer thickness, B=width of footing) ratio on the bearing capacity and settlement characteristics of the footing.